U.S. patent number 6,216,802 [Application Number 09/420,449] was granted by the patent office on 2001-04-17 for gravity oriented directional drilling apparatus and method.
Invention is credited to Donald M. Sawyer.
United States Patent |
6,216,802 |
Sawyer |
April 17, 2001 |
Gravity oriented directional drilling apparatus and method
Abstract
An apparatus for orienting a drilling assembly. In one
embodiment the apparatus include a first driveshaft coupled to the
drilling assembly, a second driveshaft flexibly coupled at one end
to the first driveshaft, and an orientation collar disposed outside
the first and second driveshafts so that the first and second
driveshafts are freely rotatable within the collar. The is collar
substantially coaxial with the first driveshaft and is adapted to
maintain a substantially fixed rotary position. The apparatus
includes a sensor for measuring the substantially fixed rotary
orientation of the collar and an adjuster for selecting a center of
rotation of the second driveshaft with respect to the axis of the
collar in response to measurements made by the sensor, whereby an
axis of rotation of the second driveshaft is selectable by changing
the center of rotation
Inventors: |
Sawyer; Donald M. (Montgomery,
TX) |
Family
ID: |
23666525 |
Appl.
No.: |
09/420,449 |
Filed: |
October 18, 1999 |
Current U.S.
Class: |
175/73;
175/61 |
Current CPC
Class: |
E21B
17/16 (20130101); E21B 47/0228 (20200501); E21B
7/067 (20130101) |
Current International
Class: |
E21B
17/16 (20060101); E21B 7/06 (20060101); E21B
47/022 (20060101); E21B 47/02 (20060101); E21B
7/04 (20060101); E21B 17/00 (20060101); E21B
007/00 () |
Field of
Search: |
;175/73,74,90,45,61,50,250,101,107 ;166/117.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pezzuto; Robert E.
Attorney, Agent or Firm: Rosenthal & Osha L.L.P.
Claims
What is claimed is:
1. An apparatus for orienting a drilling assembly, comprising:
a first driveshaft rotationally coupled to said drilling
assembly;
a second driveshaft flexibly coupled at one end to said first
driveshaft;
a radially asymmetric mass disposed outside said first and said
second driveshafts so that said first and second driveshafts are
freely rotatable within said mass, said mass substantially coaxial
with said first driveshaft; and
an adjuster for selecting a center of rotation of said second
driveshaft with respect to the axis of said mass whereby an axis of
rotation of said second driveshaft is selectively adjusted by
changing said center of rotation.
2. The apparatus as defined in claim 1 wherein said mass comprises
an asymmetrically weighted collar having substantially cylindrical
shape.
3. The apparatus as defined in claim 1 wherein said mass further
comprises a high specific gravity section and a low specific
gravity section.
4. The apparatus as defined in claim 3 wherein said high specific
gravity section comprises lead.
5. The apparatus as defined in claim 3 wherein said high specific
gravity section comprises depleted uranium.
6. The apparatus as defined in claim 3 wherein said low specific
gravity section comprises aluminum.
7. The apparatus as defined in claim 3 wherein said low specific
gravity section comprises spiral passages therethrough to resist
rotation of said eccentric mass.
8. The apparatus as defined in claim 3 wherein said low specific
gravity section comprises oil filling a space between an outer case
of said mass and an inside surface of said mass.
9. The apparatus as defined in claim 1 wherein said mass further
comprises at least one fin disposed on an exterior surface thereof
to reduce rotation of said mass from fluid flow external to said
mass.
10. The apparatus as defined in claim 1 wherein said mass further
comprises at least one jet having a discharge direction opposed to
a direction of rotation of said drilling assembly whereby rotation
of said mass is reduced by fluid discharge from said at least one
jet.
11. The apparatus as defined in claim 1 wherein said mass comprises
a sprag disposed in said mass, said sprag extending laterally from
said mass to resist rotation of said mass.
12. The apparatus as defined in claim 1 wherein said adjuster
comprises screws disposed between an outside of a bearing
supporting said second driveshaft and an inside surface of said
mass.
13. The apparatus as defined in claim 1 wherein said adjuster
comprises at least one hydraulic cylinder disposed between an outer
race of a bearing supporting said second driveshaft and an inside
surface of said mass.
14. The apparatus as defined in claim 1 wherein said adjuster
comprises a sleeve having an internal bore non-parallel with said
axis of said mass, a bearing fixed onto said second driveshaft and
supported within said non-parallel bore, a translation mechanism
for translating said sleeve with respect to said mass and a
rotation mechanism for rotating said sleeve with respect to said
mass so that a center of said bearing is adjustable with respect to
said axis of said mass by selective rotation and translation of
said sleeve with respect to said mass, thereby enabling adjustment
of said axis of rotation of said second driveshaft with respect to
said axis of said mass.
15. The apparatus as defined in claim 1 wherein said adjuster
comprises a sleeve having an helical internal bore, a bearing fixed
onto said second driveshaft and supported within said helical bore,
a translation mechanism for translating said sleeve with respect to
said mass so that a center of said bearing is adjustable with
respect to said axis of said mass by selective translation of said
sleeve with respect to said mass thereby enabling adjustment of
said axis of rotation of said second driveshaft with respect to
said axis of said mass.
16. An apparatus for orienting a drilling assembly, comprising:
a first driveshaft rotationally coupled to said drilling
assembly;
a second driveshaft flexibly coupled at one end to said first
driveshaft;
a radially asymmetric mass disposed outside said first driveshaft
so that said first driveshaft is freely rotatable within said mass,
said mass substantially coaxial with said first driveshaft; and
a sleeve disposed outside said second driveshaft, said sleeve
having an internal bore non-parallel with an axis of said mass, a
bearing fixed onto said second driveshaft and supported within said
non-parallel bore, a translation mechanism for translating said
sleeve with respect to said mass and a rotation mechanism for
rotating said sleeve with respect to said mass so that a center of
said bearing is adjustable with respect to said axis of said mass
by selective rotation and translation of said sleeve with respect
to said mass thereby enabling adjustment of said axis of rotation
of said second driveshaft with respect to said axis of said
mass.
17. An apparatus for orienting a drilling assembly, comprising:
a first driveshaft rotationally coupled to said drilling
assembly;
a second driveshaft flexibly coupled at one end to said first
driveshaft;
a radially asymmetric mass disposed outside said first driveshaft
so that said first driveshaft is freely rotatable within said mass,
said mass substantially coaxial with said first driveshaft; and
a sleeve disposed outside said second driveshaft, said sleeve
having an helical internal bore, a bearing fixed onto said second
driveshaft and supported within said helical bore, a translation
mechanism for translation of said sleeve with respect to said mass
so that a center of said bearing is adjustable with respect to an
axis of said mass by selective translation of said sleeve with
respect to said mass thereby enabling adjustment of said axis of
rotation of said second driveshaft with respect to said axis of
said mass.
18. An apparatus for orienting a drilling assembly, comprising:
a first driveshaft rotationally coupled to said drilling
assembly;
a second driveshaft flexibly coupled at one end to said first
driveshaft;
an orientation collar disposed outside said first and second
driveshafts so that said first and second driveshafts are freely
rotatable within said collar, said collar substantially coaxial
with said first driveshaft and adapted to maintain a substantially
fixed rotary position;
a sensor for measuring said fixed rotary orientation of said collar
and
an adjuster for selecting a center of rotation of said second
driveshaft with respect to the axis of said collar in response to
measurements made by said sensor whereby an axis of rotation of
said second driveshaft is selectable by changing said center of
rotation.
19. The apparatus as defined in claim 18 wherein said adjuster
comprises:
a sleeve disposed outside said second driveshaft, said sleeve
having an internal bore non-parallel with an axis of said collar, a
bearing fixed onto said second driveshaft and supported within said
non-parallel bore, a translation mechanism for translating said
sleeve with respect to said collar and a rotation mechanism for
rotating said sleeve with respect to said collar so that a center
of said bearing is adjustable with respect to said axis of said
collar by selective rotation and translation of said sleeve with
respect to said collar thereby enabling adjustment of said axis of
rotation of said second driveshaft with respect to said axis of
said collar.
20. The apparatus as defined in claim 18 wherein said fixed rotary
orientation is selectable by selectively operable mud jets, said
mud jets forming controllable hydraulic passages between a high
pressure mud passage and an annulus between said collar and a
wellbore.
21. The apparatus as defined in claim 18 wherein said sensor
generates a measurement with respect to magnetic north.
22. The apparatus as defined in claim 18 wherein said sensor
generates a measurement with respect to earth's gravity.
23. The apparatus as defined in claim 18 wherein said sensor
generates a measurement with respect to geographic north.
24. The apparatus as defined in claim 18 wherein said collar
comprises asymmetrically distributed mass therein so as to maintain
said substantially fixed rotary orientation due to earth's
gravity.
25. The apparatus as defined in claim 18 wherein said collar
comprises a sprag therein to maintain said substantially fixed
rotary orientation.
26. The apparatus as defined in claim 18 wherein said collar
comprises fins on an exterior surface thereof to maintain said
substantially fixed rotary orientation.
27. The apparatus as defined in claim 18 wherein said collar
comprises helical fluid passages therein to maintain said
substantially fixed rotary orientation.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the field of methods and
apparatus for drilling a wellbore along a desired trajectory. More
specifically, the invention relates to tools for controlling the
direction of a wellbore while drilling by rotating a drill pipe
from the earth's surface is in progress.
2. Description of the Related Art
Wellbores used for petroleum production are often drilled along
trajectories other than vertically from the earth's surface in a
process referred to as directional drilling. The main purpose of
directional drilling is for the wellbore to penetrate earth
formations at a subsurface location different from the surface
location from which the wellbore is started.
Various tools are well known in the art for directionally drilling
wellbores, including hydraulically powered motors which turn a
drill bit by converting the flow of drilling fluid ("mud") into
rotational energy, the mud flow otherwise being used to cool the
drill bit and lift drill cuttings out of the wellbore. Typical
motors designed for directional drilling purposes include a housing
which is bent at a preselected angle. These are known in the art as
"bent-housing" motors. The power generation section of such motors
is coupled to an output shaft, which ultimately turns the bit, by a
flexible coupling. When this type of motor is used to adjust the
trajectory of the wellbore, the entire drilling assembly, which
includes drill pipe, drill collars, the motor, stabilizers and the
drill bit, is slowly rotated from the earth's surface by a rotary
drilling rig or similar apparatus so that the bend of the motor
housing is oriented in the direction towards which the wellbore
trajectory is to be adjusted. As is well known in the art, after
the desired trajectory adjustment to the wellbore is finished, the
bent-housing motor must be removed from the drilling assembly. This
requires a time-consuming "trip out of the hole", where the entire
drilling assembly is removed from the wellbore and a different
assembly, which may exclude the bent-housing motor, is inserted
into the wellbore to continue drilling along the adjusted
trajectory.
In other cases, a so-called "steerable" motor can be used both to
adjust and to maintain the trajectory of the wellbore during
drilling. The typical steerable motor has a bent housing as does
the bent-housing motor, but the bend is much smaller in magnitude.
Adjusting the trajectory of the wellbore is accomplished with a
steerable motor by adjusting the orientation of the motor housing
as is done for the bent-housing motor, but when the desired
trajectory is achieved, the trajectory can be maintained by
rotating the entire drilling assembly from the earth's surface.
Rotating the housing of a steerable motor generally causes the
existing trajectory of the wellbore to be maintained.
Limitations of mud motor-based directional drilling include limited
life of the power-generation section of the typical motor, which
includes a positive displacement rotor disposed inside an
elastomeric-lined stator. An additional limitation is that
orientation of the motor housing can often be difficult to
maintain, because as the drill bit contacts the earth formations to
drill them, a reactive torque is generated against the motor
housing which changes the orientation. A particular limitation of
directional drilling using steerable motors is that steerable
motors tend to drill a "corkscrew" shaped hole where the motor
housing is rotated to maintain trajectory of the wellbore.
A different type of steerable rotary tool for directional drilling
is presented in U.S. Pat. Nos. 5,484,029 and 5,529,133 to Eddison
and U.S. Pat. No. 5,617,926 to Eddison et. al, hereafter
collectively referred to as Eddison. This steerable tool comprises
an upper housing which connects to the drill pipe and a lower
driveshaft which attaches to the drill bit. The housing and
driveshaft are coupled so that rotary torque from the housing is
transmitted to the shaft while allowing the rotational axis of the
bit to pivot universally to a limited degree relative to the
longitudinal axis of the housing. Enclosed inside the housing is an
internal "eccentric weight" arranged to have relative rotation with
respect to said housing. Due to the effects of gravity, the weight
remains substantially stationary at the low side of the directional
wellbore. The upper end of the driveshaft is coupled to the
stationary weight through an eccentric bearing to maintain the bit
axis pointed in only one direction as the bit is rotated.
Additionally, Eddison discloses an intricate clutch system used to
alter the orientation of the drill bit downhole and a
measuring-while-drilling (MWD) tool for monitoring directional
parameters with respect to the position of the weight.
SUMMARY OF THE INVENTION
The invention is an apparatus for orienting a drilling assembly.
The apparatus includes a first driveshaft coupled to the drilling
assembly, a second driveshaft flexibly coupled to the first
driveshaft, and an orientation collar disposed outside the first
and second driveshafts so that the first and second driveshafts can
rotate freely inside the collar while the collar remains
rotationally fixed. The collar is substantially coaxial with the
first driveshaft. The apparatus includes an adjuster for selecting
a center of rotation of the second driveshaft with respect to an
axis of the collar so that an axis of rotation of the second
driveshaft is selected by changing the position of the center of
rotation.
In one embodiment, the adjuster includes screws to set the position
of a bearing disposed on the outside of the second driveshaft to
change the position of a center of rotation of one point on the
second driveshaft. In another embodiment, the adjuster includes a
sleeve having a bore non-parallel with the axis of the collar, and
a rotation and translation mechanism to slide and rotate the sleeve
with respect to the collar. The bearing supporting the lower
driveshaft is supported in the bore, so that changing the position
and rotary orientation of the sleeve changes the relative angle of
the second driveshaft with respect to the center line of the
collar.
The collar in one embodiment is oriented by earth's gravity because
the collar has asymmetric mass about its center line. The collar in
various embodiments includes devices to resist rotation of the
collar including vanes, mud discharge jets and a sprag which
contacts the wellbore wall.
In another embodiment, the orientation of the collar is measured,
and the relative angle of rotation of the second driveshaft with
respect to the center line of the collar is adjusted in response to
the measured orientation. In this embodiment, the collar can
include various devices to resist rotation thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows one embodiment of the invention in cross-section as it
is used to directionally drill a wellbore penetrating earth
formations.
FIG. 2 shows one embodiment of an orientation collar for the
invention, which is an asymmetrically weighted collar.
FIG. 3 shows the embodiment of FIG. 2 in cross-section.
FIG. 4A shows embodiments of several improvements to the
orientation collar of FIG. 2, which reduce the tendency of the
asymmetrically weighted collar to rotate as a result of fluid
friction between the collar and a driveshaft.
FIG. 4B shows another embodiment of an improvement used to reduce
rotation of the collar.
FIGS. 5A and 5B show an embodiment of a sleeve used to adjust the
orientation of the drill bit with respect to asymmetrically
weighted collar.
FIG. 6 shows an alternative embodiment of the collar.
DETAILED DESCRIPTION
FIG. 1 shows one embodiment of the invention as it is to be used to
directionally drill a wellbore through earth formations. The
wellbore is shown generally at 2 as it has been drilled through the
earth formations, shown generally at 4. The wellbore 2 can be
drilled using a rotary drill bit 30 of any type well known in the
art.
As is well known in the art, rotary power to turn the drill bit 30
can be provided by a drilling rig (not shown) or the like located
on the earth's surface. The drilling rig (not shown) is typically
coupled to the drill bit 30 by a drilling assembly which includes
sections of threaded drill pipe, one section of which is shown at
6. As is also well known in the art, the drill pipe 6 can include,
generally at the bottom end, larger diameter, high-density sections
known as "heavy-weights" or "drill collars" which increase the
bottom-end weight of the drilling assembly so that earth's gravity
can assist in providing axial force to the drill bit 30. A drilling
assembly which includes only drill pipe 6, collars, the bit 30, and
centering tools known as stabilizers, shown generally at 8 and 28,
will follow a trajectory affected by gravity, the flexibility of
the drilling assembly and the mechanical properties of the earth
formations 4 through which the well is drilled. The rotational axis
(not shown) of the drill bit 30 in such drilling assemblies is
substantially coaxial with the center line 10 of the drilling
assembly, not taking account of any flexibility of the drilling
assembly.
Directional drilling systems, such as described in the Background
section herein, cause the rotational axis (not shown) of the drill
bit 30 to be deflected from the center line (rotational axis) 10 of
the drill pipe 6 in a selected direction. This embodiment of the
invention, shown generally at 32 and for convenience referred to
hereafter as a "steering system", provides an improved mechanism to
place the axis of rotation of the drill bit 30 along such a
selected direction.
The principal components of this embodiment of the steering system
32 include an orientation collar, shown at 16 in FIG. 1. The
purpose of the orientation collar 16 is to provide a rotationally
fixed reference against which to set an axis of rotation of the
drill bit 30, as will be further explained. In this embodiment, the
orientation collar 16 is an asymmetrically weighted collar ("AWC"),
which includes means of bearings 12, 18 and 20 to enable free
rotation within the orientation collar 16 of an upper driveshaft 14
and a lower driveshaft 24. As will be further explained, in this
embodiment the orientation collar 16 is asymmetric in mass radially
or circumferentially about its axis (that is, it is rotationally
unbalanced) so that one side of the orientation collar 16 will tend
to rest downwardly, that is, in the direction of gravity. The
asymmetry of the mass of the orientation collar 16 in this
embodiment provides one element of the steering system 32 which is
substantially rotationally fixed during drilling. Components which
are rotationally coupled to the collar 16, which will be further
explained, will thus be oriented with respect to earth's
gravity.
Rotary torque can be transmitted from the drilling rig (not shown)
at the earth's surface directly to the bit 30 through the steering
system 32. The upper driveshaft 14 is coupled at one end to the
drill pipe 6, optionally through upper stabilizer 8. The upper
driveshaft 14 can be flexibly coupled to the lower driveshaft 24 by
means of a universal joint, flexible coupling, constant velocity
joint or any similar flexible rotary connection, shown generally at
22, which enables transmission of rotary torque across a change in
direction of the axis of rotation. The upper driveshaft 14 rotates
substantially collinearly with the drill pipe 6 immediately
connected thereto because it is held in position relative to the
collar 16 by the upper bearing 12 and center bearing 18, both of
which are positioned substantially collinearly with the collar 16.
The lower driveshaft 24 can be coupled through lower stabilizer 28
to the bit 30, through a mud motor (not shown) or any other
drilling tools. Selection of and location of stabilizers 8, 28 in
the drilling assembly depends on the intended trajectory of the
wellbore as is known in the art, and such placements of stabilizers
and drilling tools are not intended to limit the invention.
In the invention, the orientation of the axis of rotation of the
lower driveshaft 24 with respect to the center line 10 of the
orientation collar 16 is generally changed by changing the position
of the center of the lower bearing 20 with respect to the center
line 10 of the orientation collar 16, as will be further explained.
The orientation of the axis of rotation of the lower driveshaft 24
will thus be determined by the relative position of the lower
bearing 20 with respect to the center line 10 of the orientation
collar 16.
In one embodiment of the invention, the position of the lower
bearing 20 can be changed by means of adjusting screws, shown
generally at 26. The adjusting screws 26 are preferably located in
the lower part of the orientation collar 16, whereby an outer case
of the collar 16 serves as a fixture against which to adjust the
position of the lower bearing 20. The means used to adjust the
position of the lower bearing 20 with respect to the center of the
collar 16 shown in FIG. 1 is only one example of possible
adjustment means. The means actually used to adjust the position of
the lower bearing 20 with respect to the center of the collar 16 is
a matter of convenience for the system designer and is not meant to
limit this aspect of the invention.
With respect to the example shown in FIG. 1, while the adjuster for
setting the position of the lower bearing 20 is fixed, in another
aspect of the invention, an adjuster which can be operated while
the steering system 32 is in the wellbore 2 can also be used. For
example, a sliding sleeve adjuster 34 having an internal bore 29
which is not parallel to the center line 10 of the orientation
collar 16 can be used to adjust the center position of the lower
bearing 20 with respect to the center line 10 of the collar 16, as
shown in FIGS. 5A and 5B. Using the sliding sleeve 34 having such a
non-parallel internal bore 29, the angular displacement of the bit
30 can be adjusted by axially displacing the sleeve 34 relative to
the orientation collar 16 until the desired magnitude of the angle
of lower shaft 24 with respect to the center line 10 of the
orientation collar 16 is selected. This is illustrated in FIGS. 5A
and 5B, wherein the sleeve 34 can be translated from a first
position 44A (FIG. 5A), to a second position 44B (FIG. 5B), thereby
adjusting the magnitude of the angle of the lower shaft 24 with
respect to the center line 10 of the collar 16. Rotating the sleeve
34 relative to the collar 16 provides the desired azimuthal
orientation of the bit 30 with respect to the orientation of the
collar 16. Mechanisms for translating and rotating the sliding
sleeve 34 with respect to the collar 16 are known in the art. One
example of such a translation and rotation mechanism is shown in
FIGS. 5A and 5B, wherein the sliding sleeve 34 uses worm gears 36
driven by motors M1B, M2B for translation, and spur gears 38 driven
by motors M1A, M2A in meshing engagement with gear teeth 40 on the
collar 16 for rotation. Alternatively, hydraulic actuation or other
means may be used. The actual translation and rotation means used
with the sliding sleeve 34 are a matter of convenience for the
system designer and are not meant to limit this invention.
Additionally, the shape of the bore 29 of the sliding sleeve need
not be a straight as shown in FIGS. 5A and 5B. Alternatively an
increasing-helix radius helical bore (not shown) can be used
wherein the sleeve 34 may simply be axially displaced to adjust
both the angle magnitude and azimuthal orientation of the lower
shaft 24, and consequently the drill bit 30, with respect to the
center line (10 in FIG. 1) of the collar 16.
Referring once again to FIG. 1, alternatively, an hydraulic
cylinder type adjuster (not shown) could be disposed between the
outer race of the lower bearing 20 and the collar 16 to adjust the
center position of the lower bearing 20 with respect to the center
line 10 of the collar 16.
The hydraulic cylinder-based adjuster, as well as the sleeve
adjuster shown in FIGS. 5A and 5B can be configured, using control
circuits well known in the art, to be responsive to measurements
from a measurement-while-drilling (MWD) system (not shown) forming
part of the drilling assembly, or to be responsive to drilling mud
pressure-based command signals sent from the earth's surface. Such
remotely operable adjusters make possible both wellbore trajectory
adjustments during drilling, and trajectory maintenance settings
where the center of rotation of the lower bearing 20 is set to be
axially parallel with the center line 10 of the orientation collar
16, so that the extant trajectory of the wellbore 2 will be
maintained.
The orientation collar 16 and components running through it are
shown in more detail in FIGS. 2 and 3. In FIG. 2, the collar 16 can
include the previously mentioned case 16A which in this embodiment
can be a steel pipe or the like preferably being cylindrically
shaped and having an outside diameter comparable to that of the
drill pipe (6 in FIG. 1) connected to the upper driveshaft 14. For
example, if the portion of the drill pipe (6 in FIG. 1) connected
to the upper driveshaft is a 6.75 inch (171.45 mm) O. D. "heavy
weight" or "drill collar", then the case 16A preferably has the
same 6.75 inch (171.45 mm) outside diameter to maintain overall
stability of the drilling assembly. It should be understood,
however, that the shape of and the outside diameter of the case 16A
is a matter of convenience for the system designer and is not meant
to limit the invention. The upper driveshaft 14, as well as the
lower driveshaft 24 preferably include a centrally located passage
or bore 14A through which the drilling mud can flow.
The inner diameter of the case 16A, although its actual dimension
is not critical to the invention, should preferably be selected to
provide a space 14B for the bearings 12, 18, 20 between the inner
diameter of the case 16A and the outer diameter of the driveshafts
14, 24. The inner diameter of the case 16A should also be as small
as is practical, as should be the outside diameter of the
driveshafts 14, 24, to enable the mass of the collar 16 to be as
large, and as asymmetric about the axis of rotation as possible,
consistent with the need for of adequate bending stiffness of the
driveshafts 14, 24 and of the overall drilling assembly, and
consistent with the driveshafts 14, 24 having the capacity to
transmit adequate rotary torque to the bit (30 in FIG. 1) without
breaking.
The case 16A in this embodiment includes therein a high specific
gravity section, shown generally at 16B. The high specific gravity
section 16B is shown as subtending about half the total
circumference of the case 16A, but it should be understood that the
amount of the circumference subtended by the high specific gravity
section 16B is a matter of convenience for the system designer and
is not meant to limit the invention. The actual shape of the high
specific gravity section 16B is also a matter of convenience, and
the generally cylindrical-section shape shown in FIG. 2 should not
be construed as a limitation on the invention. A cross-section of
the collar 16, including the case 16A, the high specific gravity
section 16B and a corresponding low specific gravity section 16C,
is shown in FIG. 3. The high specific gravity section 16B can be
formed, for example, by filling the part of the case 16A with very
dense materials such as lead, depleted uranium or the like. The low
specific gravity section 16C may be merely enclosed air space, but
preferably includes filling that portion of the case 16A with a low
density, relatively incompressible material, such as oil or
aluminum for example, so that the case 16A will resist crushing
under hydrostatic pressure in the passage 14A and in the wellbore
(4 in FIG. 1). The high specific gravity section 16B will tend to
rest in the direction of gravity, providing a rotationally fixed
reference against which to set the position of the lower bearing 20
with respect to the center of the collar 16. As previously
explained, setting the position of the center of the lower bearing
20 at a known location from the center of the orientation collar 16
provides an axis of rotation for the lower driveshaft 24 which is
different from the axis of rotation of the upper driveshaft 14 and
which is oriented in a known, selected direction with respect to
the known rotational reference, i. e. earth's gravity.
Additional features which can reduce the tendency of the
orientation collar 16 to be rotated by fluid friction between the
driveshafts (14, 24 in FIG. 1) and the collar 16 are shown in FIG.
4A. In one such improvement, the low specific gravity section 16C,
where filled with a solid such as aluminum, for example, can
include spiral passages 17 therethrough which can be hydraulically
connected to the passage (14B in FIG. 2). Fluid inertia of the mud
flowing in the spiral passages 17 can reduce the tendency of the
orientation collar 16 to rotate away from its gravitational
orientation.
Another such improvement can include helically spaced-apart vanes
or fins 19 disposed on the exterior of the case 16A so that fluid
flow up the annulus (2 in FIG. 1) will tend to stabilize the
rotational position of the collar 16.
Still another improvement can include jets 21 formed through the
collar 16 which interconnect the passage (14B in FIG. 2) and the
annulus (4 in FIG. 1) and have a discharge direction such that
drilling mud discharged through the jets 21 will create a thrust
tending to oppose fluid-friction induced rotation of the collar 16
in the direction of rotation 23 of the drill pipe (6 in FIG.
1).
Still another example of an improvement to the case 16A used to
resist rotation of the case 16A while drilling is shown in FIG. 4B.
The case 16A includes in the heavy weight section 16B a sprag 19
which can extend by gravity so that friction teeth 21 disposed on
the outside of the sprag 19 can contact the wall of the wellbore.
Lateral movement of the sprag 19 can be limited by pins 23 loaded
by springs 25 to mesh in mating slots 27 in the sprag 19, the slots
27 being shaped to enable the sprag 19 to move laterally inward,
but also to limit lateral outward movement of the sprag 19 from the
case 16A. The sprag 19 shown in this example is actuated by
gravity, but it should be clear to those skilled in the art that
powered forms of actuation for the sprag, such as hydraulic
cylinders, solenoids, springs or the like can also be used to
extend the sprag 19 laterally from the case 16A.
The preceding embodiments of the orientation collar 16 rely on
earth's gravity to orient the collar 16. As previously explained,
the orientation of the collar 16 is used as a fixed reference
against which to set the position of the bearing supporting the
lower driveshaft (20 in FIG. 1). By setting the position of the
lower bearing 20 with respect to the collar 16, the magnitude and
direction of the angle of the second driveshaft can be set with
respect to the center line of the collar 16. In the present
embodiment of the collar 16, the collar 16 need not include
asymmetric mass but can have its relative orientation determined by
means other than earth's gravity. Referring now to FIG. 6, the
present embodiment of the orientation collar will be explained. The
orientation collar in this embodiment is shown generally at 116 and
is formed generally in the shape of a cylinder. A first driveshaft
114, which is similar to the first driveshaft in the other
embodiments of the invention, rotates inside the collar 116 on
bearings 112, 118. The first driveshaft, as previously explained,
is rotated by a drilling rig, mud motor or similar rotary power
source. The orientation collar 116 in this embodiment can be
symmetric in mass distribution, to enable the collar 116 to be
freely rotated irrespective of its orientation with respect to
gravity. As in the previous embodiments of the invention, the first
driveshaft 114 is flexibly coupled to a second driveshaft 124
through a flexible coupling. The second driveshaft 124 can be
supported by a lower bearing (not shown in FIG. 6) disposed in an
adjuster mechanism (not shown in FIG. 6) similar to those described
in the previous embodiments (such as 20 in FIG. 1). In the present
embodiment, the adjuster mechanism (not shown) works in
substantially the same manner as in the previous embodiments shown
in FIGS. 5A and 5B, and for clarity of the description will not be
repeated here.
In the present embodiment, the first driveshaft 114 can include
therein slots or perforations 130 which enable passage of
pressurized drilling mud 128 pumped from the surface to flow out of
the first driveshaft 114 and pressurize the annular space between
the collar 116 and the first driveshaft 114, axially between
bearings 112 and 118. The pressurized mud is selectively vented to
an annular space between the collar 116 and a wellbore (not shown)
through discharge jets 132 and 136. When the pressurized mud is
discharged through jets 132, the collar 116 will tend to rotate in
the direction opposite to the mud flow therethrough. Jets 136 are
positioned to cause the opposite rotation of the collar 116 when
mud is vented therethrough. By selective venting of the pressurized
mud through the jets 132, 136, the collar 116 can be rotated to to
a selected rotary orientation, and the selected rotary orientation
can be maintained.
The control of pressurized mud venting through the jets 132, 136
can be performed by selectively operable valves 134A, 134B,
respectively. The valves 134A, 134B operate in response to a
directional sensor 130. The directional sensor 130 can be a
magnetometer, accelerometers, gyroscope or any other device which
makes measurements corresponding to the orientation of the sensor
with respect to a fixed reference, such as magnetic north,
geographic north or earth's gravity, for example. The output of the
sensor 130 is used to selectively operate the valves 134A, 134B to
maintain the selected rotary orientation of the collar 116. Other
types of mechanisms for rotating the collar 116 to maintain rotary
orientation can be used in place of the jets 132, 136, for example
tractor pads or the like.
Still other embodiments of the orientation collar need not include
the jets 132, 136 shown in FIG. 6 or other device to select the
orientation of the collar 116. Instead, the collar 116 may include
the anti-rotation devices shown in FIGS. 4A and 4B to maintain the
collar 116 in a rotationally fixed position. Where jets or other
devices to select a rotary orientation are not used, it is
preferable to include a sensor, such as 130 in FIG. 6, to measure
the extant orientation of the collar 116. The orientation and angle
magnitude applied to the lower driveshaft 124 by the adjuster (such
as 34 in FIGS. 5A and 5B) can be set in response to the measured
orientation of the collar 116, to provide a selected change in
direction of drilling the wellbore. Note that in this embodiment,
it is not necessary to set the orientation of the collar, it is
only necessary to determine the orientation and to set the
orientation and angle magnitude of the adjuster (such as 34 in FIG.
5A) in response to the determined orientation.
It will be apparent to those skilled in the art that the foregoing
description is only intended to illustrate examples of the
invention, and that those skilled in the art will be able to devise
other embodiments of the invention which do not depart from the
spirit of the invention as disclosed in the embodiments described
herein. Accordingly, the scope of the invention shall be limited
only by the attached claims.
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